The Morphology Core is dedicated to supporting each of the specific proposals in this project from the following aspects: 1.) Assessment of viability of transfected hepatocytes in vitro and in vivo; 2.) Identification and quantitation of transplanted cells in recipients; and 3.) Assessment of short and long-term pathological alterations in recipients subjected to surgical (delivery) procedures, retrovirus vectors, foreign genes. The several components of the project, involving multiple animal species (rabbit, dog, mouse and pig), harvesting of hepatocytes, their growth in culture, virus-mediated gene transfer and transplantation by each of several surgical routes, all require a contribution from this core. The methods to be used include: 1.) Routine histology to provide standard sections and stains on paraffin-embedded fixed tissues; 2.) Immunohistochemistry with vacuum embedding at low temperature to maximize antigen (protein) and mRNA preservation; 3.) Frozen sections for immunochemistry, enzyme histochemistry and radioautography providing for a variety of markers of gene expression (ie: E. coli beta-galactosidase, mRNA in situ); 4.) Transmission and scanning electron microscopy for characterization of cell type and cell preservation; and 5.) Immunoelectron microscopy for localization of gene products as measure of functional integrity and orderly expression (ie: alpha1 antitrypsin, CAT) and for detection of retroviral products.